In recent years, surgical instruments of disposable type being thrown away after one use without being washed for reuse have become widespread for reasons such as the problem of infection and the troublesome washing and disinfection. As for the endoscope, there is a demand for a low-priced disposable type.
To meet this demand, a disposable endoscope has been proposed which can be inexpensively manufactured because of the insertion portion employing a structure in which an imaging optical system for forming a subject image and an illumination optical system for illuminating the subject are integrated by use of resin.
Moreover, an optical inspection tube has been proposed which is suitable for use as a disposable endoscope because an optical pipe made of a polymeric material such as acrylic is used as a light guide and a similar polymeric material is used as the material of other structural elements such as the objective lens and the relay lens.
An example of the above-mentioned endoscope will hereinafter be described with reference to the drawings.
FIG. 15(A) is a cross-sectional view of an insertion portion of an endoscope shown in Japanese Laid-open Patent Application No. H6-254049. FIG. 15(B) is a general structural view of the endoscope.
As shown in FIG. 15(B), an endoscope 101 is an electronic endoscope having a CCD 117 at its front end portion, and has an insertion portion 102 to be inserted in the observation portion of the subject. The insertion portion 102 is connected through a cable 125 to a light source apparatus 130 for supplying illumination light to the insertion portion 102 and to a CCU 129 for processing image sensing signals from the CCD 117. The insertion portion 102 and the cable 125 are electrically connected by engaging male pins 121 of an video connector 120 with female pins of a corresponding video connector 120 of the connector 107 of the cable 125. The insertion portion 102 is formed, as shown in FIG. 15(A), by integrating by use of a resin 108 an illumination optical system comprising a light guide 112 for transmitting the illumination light and an illumination lens 118, an observation optical system comprising a plurality of objective lenses 113 and 114, the CCD 117 and a signal line 123. Since the insertion portion 102 is inexpensively manufactured because of this structure, it can be thrown away after one use.
FIG. 16(A) is a side cross-sectional view of an endoscope shown in Japanese Patent Kohyo No. H2-503361. FIG. 16(B) is an exploded perspective view of the endoscope and shows a series of rod lenses placed from one end to the other inside a molded optical pipe. FIG. 16(C) is a cross-sectional view showing in detail the position of one of the rod lenses placed inside the optical pipe.
As shown in FIG. 16, an optical inspection apparatus 210 is an optical inspection tube for an inspector 212 to inspect an area 224 in a body cavity, and has inside an elongated optical pipe 214 for directing light from a light source 220. The optical pipe 214 has an elongated portion extending from a distal end 218 of the pipe to a bending portion in the vicinity of a proximal end 216 of the pipe, and has an elongated cradle-shaped concave portion 254 inside the elongated portion. The lens units such as relay lens units 238 are first fixed in the concave portion 254 of the optical pipe 214 and then inserted into a pipe 258 made of aluminum. Then, their centers are aligned with each other and the insertion portion is completed. By using ones molded from a polymeric material such as acrylic as structural elements such as the optical pipe 214, objective lens units 222 and the relay lens units 238, a structure suitable for use as a disposable endoscope is achieved.
However, the endoscope having the above-described structure has the following problems:
(1) Since the light guides 112 and 214 for transmitting the illumination light are provided separately from the exterior structures 108 and 258 of the insertion portions 102 and 210, the cost increases and the assembly process is complicated.
(2) In the case of a disposable endoscope, if a material which cannot be incinerated such as a metal and glass is used for the exterior structure of the insertion portion and the light guide, medical waste increases.
(3) When an electric connection portion for transmitting video signals and a light directing cable connection portion for transmitting the illumination light are separately provided and taken out from different directions, it is necessary for the light directing member to have a bending configuration, so that the assembly and the connection are complicated. In addition, the configuration of the operation portion of the endoscope is complicated, so that easy operation cannot be achieved.
(4) Since the CCD is aligned with the objective lens and inserted into the insertion portion of the endoscope under a condition where the CCD is connected to the signal line, handling is not easy and the assembly process is complicated.
Since the pin-shaped connector conventionally used as the electric connection portion for transmitting video signals has a structure unsuitable for enabling easy connection and disconnection and it is necessary to provide a connector also on the side of the insertion portion, the price increases.
(5) Since parts which require positioning and fixing such as the objective optical system, the imaging optical system and the image sensing optical system are necessarily positioned and fixed in advance with screws before inserted into the insertion portion of the endoscope, and a dedicated mounting member and drilling of holes for fixing are necessary, the structure of the insertion portion is intricate and the assembly process is complicated.
FIG. 21 is a structural view of an insertion portion of an endoscope proposed in Japanese Laid-open Patent Application No. H8-122663.
This endoscope comprises a light guide 61 formed of a silica optical fiber bundle for transmitting the illumination light, a light diffusing device 62 for diffusing the illumination light having exited from an end surface 61a of the light guide 61 and an image sensing optical system 63 for image-sensing reflected light from the subject.
The light diffusing device 62 is used for distributing the intensity of the illumination light for illuminating the subject so as to have desired characteristics. Examples of the conventional light diffusing device 62 include a concave lens using a grinding technology, a hologram lens using a holography technology, and an LSD (light shaping diffuser) optical device using a refraction effect of light and manufactured and marketed by POC (Physical Optics Corporation) of the United States.
By using the light diffusing device 62, it has been attempted to improve the illumination distribution such that the central portion of the sensed area is bright and the peripheral portion thereof is dark.
However, the endoscope using the light diffusing device as described above has the following problems:
(6) Since the concave lens requires grinding, the cost is extremely high.
(7) Since the hologram lens diffuses the illumination light by use of a diffraction phenomenon of light, the color reproducibility is inferior, so that nonuniformity is caused in color.
(8) In the case of the one comprising the LSD, although the nonuniformity in color is not caused, the cost increases because it is necessary to dispose it as a separate member in the vicinity of an end surface of the light guide so as to be exclusively used for that purpose.
(9) Since only the light having exited from an end surface of the optical fiber bundle is diffused, the diffusion effect is limited, so that it is difficult to obtain a desired illumination distribution.